Gangliosides that are present on the platelet surface and thus conceivably regulate platelet physiological activities will be identified by using an external labeling technique utilizing galactose oxidase. This approach also will be used to detect subtle changes in the arrangement of gangliosides on the surface of platelets activated by thrombin and other aggregating agents. The location of phosphatidylinositol and phosphatidlethaolamine in the platelet plasma membrane lipid bilayer will be determined by evaluatin the susceptibility of these phospholipids to non-penetrating selective enzymatic and chemical membrane probes. The physiological role of platelet membrane neutral glycolipids and gangliosides will be investigated by the analysis of the effects of specific antiglycosphingolipid antibodies on platelet function. The consequences of increasing the content of specific platelet plasma membrane gangliosides by the incorporation of exogenously supplied gangliosides also will be investigated. The function of platelet plasma membrane phosphatidylinositol and phosphatidylethanolamine will be probed by the evaluation of the consequences of their selective enzymatic modification. The effects of these alterations and modifications of platelet membrane glycosphingolipids and phospholipids will be assessed on platelet functions, e.g., adhesion to collagen, aggregation, the release reaction, as well as on serotonin and alpha adrenergic receptor binding in platelets. Platelets from patients with disorders in which there is a high probability of abnormal platelet membrane glycosphingolipids, e.g., myeloproliferative syndromes, type II hyperlipidemia, and the Bernard Soulier syndrome, will be investigated. Platelets from these individuals will be evaluated for abnormal gangliosie and neutral glycolipid composition and structure. The fatty acid, sphingosine, and carbohydrate components of these glycosphingolipids will be analyzed by gas-liquid chromatography.